The present invention is directed toward mechanical and/or chemical-mechanical planarization of microelectronic-device substrate assemblies. More specifically, the invention is related to planarizing pads, planarizing machines and methods for optically monitoring the status of a microelectronic-device substrate assembly during a planarizing cycle.
Mechanical and chemical-mechanical planarizing processes (collectively xe2x80x9cCMPxe2x80x9d) remove material from the surface of semiconductor wafers, field emission displays or other microelectronic substrates in the production of microelectronic devices and other products. FIG. 1 schematically illustrates a rotary CMP machine 10 with a platen 20, a carrier assembly 30, and a planarizing pad 40. The CMP machine 10 may also have an under-pad 25 attached to an upper surface 22 of the platen 20 and the lower surface of the planarizing pad 40. A drive assembly 26 rotates the platen 20 (indicated by arrow F), or it reciprocates the platen 20 back and forth (indicated by arrow G). Since the planarizing pad 40 is attached to the under-pad 25, the planarizing pad 40 moves with the platen 20 during planarization.
The carrier assembly 30 has a head 32 to which a substrate 12 may be attached, or the substrate 12 may be attached to a resilient pad 34 positioned between the substrate 12 and the head 32. The head 32 may be a free-floating wafer carrier, or the head 32 may be coupled to an actuator assembly 36 that imparts axial and/or rotational motion to the substrate 12 (indicated by arrows H and I, respectively).
The planarizing pad 40 and the planarizing solution 44 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate The planarizing pad 40 can be a fixed-abrasive planarizing pad in which abrasive particles are fixedly bonded to a suspension material. In fixed-abrasive applications, the planarizing solution is typically a non-abrasive xe2x80x9cclean solutionxe2x80x9d without abrasive particles. In other applications, the planarizing pad 40 can be a non-abrasive pad composed of a polymeric material (e.g., polyurethane), resin, felt or other suitable non-abrasive materials. The planarizing solutions 44 used with the non-abrasive planarizing pads are typically abrasive slurries with abrasive particles suspended in a liquid.
To planarize the substrate 12 with the CMP machine 10, the carrier assembly 30 presses the substrate 12 face-downward against the polishing medium. More specifically, the carrier assembly 30 generally presses the substrate 12 against the planarizing liquid 44 on the planarizing surface 42 of the planarizing pad 40, and the platen 20 and/or the carrier assembly 30 move to rub the substrate 12 against the planarizing surface 42. As the substrate 12 rubs against the planarizing surface 42, material is removed from the face of the substrate 12.
CMP processes should consistently and accurately produce a uniformly planar surface on the substrate to enable precise fabrication of circuits and photo-patterns. During the construction of transistors, contacts, interconnects and other features, many substrates develop large xe2x80x9cstep heightsxe2x80x9d that create highly topographic surfaces. Such highly topographical surfaces can impair the accuracy of subsequent photolithographic procedures and other processes that are necessary for forming sub-micron features. For example, it is difficult to accurately focus photo patterns to within tolerances approaching 0.1 micron on topographic surfaces because sub-micron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes are often used to transform a topographical surface into a highly uniform, planar surface at various stages of manufacturing microelectronic devices on a substrate.
In the highly competitive semiconductor industry, it is also desirable to maximize the throughput of CMP processing by producing a planar surface on a substrate as quickly as possible. The throughput of CMP processing is a function, at least in part, of the ability to accurately stop CMP processing at a desired endpoint. In a typical CMP process, the desired endpoint is reached when the surface of the substrate is planar and/or when enough material has been removed from the substrate to form discrete components on the substrate (e.g., shallow trench isolation areas, contacts and damascene lines). Accurately stopping CMP processing at a desired endpoint is important for maintaining a high throughput because the substrate assembly may need to be re-polished if it is xe2x80x9cunder-planarized,xe2x80x9d or components on the substrate may be destroyed if it is xe2x80x9cover-polished.xe2x80x9d Thus, it is highly desirable to stop CMP processing at the desired endpoint.
In one conventional method for determining the endpoint of CMP processing, the planarizing period of a particular substrate is determined using an estimated polishing rate based upon the polishing rate of identical substrates that were planarized under the same conditions. The estimated planarizing period for a particular substrate, however, may not be accurate because the polishing rate or other variables may change from one sabstrate to another. Thus, this method may not produce accurate results.
In another method for determining the endpoint of CMP processing, the substrate is removed from the pad and then a measuring device measures a change in thickness of the substrate. Removing the substrate from the pad, however, interrupts the planarizing process and may damage the substrate. Thus, this method generally reduces the throughput of CMP processing.
U.S. Pat. No. 5,433,651 issued to Lustig et al. (xe2x80x9cLustigxe2x80x9d) discloses an in-situ chemical-mechanical polishing machine for monitoring the polishing process during a planarizing cycle. The polishing machine has a rotatable polishing table including a window embedded in the table. A planarizing pad is attached to the table, and the pad has an aperture aligned with the window in the table. The window is positioned at a location over which the workpiece can pass for in-situ viewing of a polishing surface of the workpiece from beneath the polishing table. The planarizing machine also includes a device for measuring a reflectance signal representative of an in-situ reflectance of the polishing surface of the workpiece. One drawback of the device disclosed in Lustig is that slurry may seep under the pad adjacent to the aperture. The slurry may accordingly contaminate the backside of the pad or the platen in a manner that affects the consistency of the planarizing process, reduces the life of the pad, and increases maintenance for cleaning.
Another oral endpointing system is a component of the Mirra(copyright) planarizing machine manufactured by Applied Material Corporation of California. The Mirra(copyright) machine has a rotary platen with an optical emitter/sensor and a planarizing pad with a window over the optical emitter/sensor. Although the Mirra(copyright) machine is an improvement over many other endpointing systems, the planarizing solution can leak through the interface between the pad and the window. The Mirra(copyright) machine, therefore, may also produce inconsistent results, require more maintenance because the backside of the pad and the platen may be contaminated, and reduce the life of the pad because the abrasive particles can wear away the backside of the pad.
The present invention is directed toward planarizing pads, planarizing machines and methods for manufacturing and using planarizing pads in mechanical and/or chemical-mechanical planarization of microelectronic-device substrate assemblies. In one embodiment of a planarizing machine, the machine includes a table having a support surface and an optical monitoring system coupled to the table. The table, for example, can be a rotary platen or a stationary support surface having an opening at an illumination site. The optical monitoring system can have a light source and an optical sensor aligned with the opening in the table to direct and detect a light beam through the opening.
The planarizing machine can further include a planarizing pad coupled to the support surface of the table. The planarizing pad comprises a planarizing medium, an optically transmissive window in the planarizing medium, and a backing member attached to the planarizing medium. The planarizing medium can have a planarizing surface, a backside opposite the planarizing surface, and at least one hole extending from the planarizing surface to the backside. The hole in the planarizing medium generally has a sidewall transverse to the backside. The backing member has a top surface attached to the backside of the planarizing medium and an exposed section extending from the sidewall to either (a) span completely across the hole or (b) project across a portion of the hole for a cover distance that is measured normal to the sidewall. The optically transmissive window is positioned in the hole, and it has an interface surface contacting the exposed section o backing member. The interface surface of the window generally contacts the exposed section along a seal path that either spans completely across the hole or extends along a length greater than the cover distance.
The planarizing machine can further include a carrier assembly having a head and a drive mechanism. In operation, a planarizing solution is disposed on the planarizing surface of the planarizing medium, and then either the head of the carrier system and/or the planarizing pad move in a planarizing plane to rub the substrate against the planarizing medium. The optically transmissive window and the backing member are configured to inhibit or eliminate the planarizing solution from leaking through the planarizing pad. Additionally, the optically transmissive window and the backing member are generally discrete components comprising different materials to take advantage of particular optical, and planarizing properties of the window and to also take advantage of the durability and other properties of the backing member.